White Paper: A Mission Critical Document
01/01/2000
JIM ANGELONI
The purpose of a "white paper" is to ensure compliance of a particular product being built to a customer`s specifications - to validate product and process by optimizing and verifying them at the pre-production stage. Additionally, information derived and presented as part of a white paper is based on statistically sound and valid data, thus it establishes the best-known method (BKM) for producing a particular product. The BKM will achieve optimum product production repeatability, product quality
eliability and product manufacturing performance. The need for a repeatable process, especially when that process is applied to highly automated surface mount technology (SMT) and multichip module (MCM) production lines, is critical to end product success. At the rate that a product is built on automatic lines, process repeatability must be ensured. Thus, the amount of time required to characterize, develop and complete a white paper is fully justified over the life of a product.
To Begin
The responsibility for creating a white paper starts with process engineering. However, the customer, quality and production departments are also key to establishing white paper requirements.
The basic elements of a white paper are:
- Description of the product and reason for the paper. Reasons can be starting a new product, changing an existing product, or adding new equipment to a product line.
- Documents and specifications affected
- A qualification plan
- A process plan, including a mechanical test plan and results table, an electrical test plan and results table, an environmental test plan and results (not always required), a pre-production plan (if required), and an implementation plan.
Obviously, you can add or remove particular elements of a white paper specific to your company`s or customer`s requirements.
Once a paper has been developed and the key elements agreed to, it is reviewed by the customer to ensure that all of the customer`s concerns and requirements are covered.
The Qualification Plan
In this section of a white paper, a plan is developed that describes the number of parts to be built and tested, how the parts should be grouped and the times that the parts are built. The key element of the qualification plan is the mechanical test and results table. In this section, a table is developed that lists mechanical tests to be done, the limits of each test and actual test results (Table 1). Typically, a minimum of three lots of 25-50 parts per lot are used. However, only 3-5 parts per lot are used for the mechanical tests. (Note that each lot should be run on different shifts or production days.)
The object of this requirement is to establish the repeatability of a process when equipment is shut down, personnel are changed and equipment is restarted on different shifts. Assuming that the data is acceptable, the balance of these lots are good parts. It is important to note that, prior to starting this type of qualification, the various process steps should have been characterized to establish the correct parameter setting for each process step.1 Typically, process variability at each process step varies greatly. Even though process variability is reduced when products are built on a highly automated line, process characterization is still a must. A white paper will ensure compliance to the process characterization results and customer requirements via the data obtained.
In the event that a particular test fails to meet the limits set by a white paper, an investigation of the process parameters for that test must be compared to the characterization data that originally set up the process. If a mistake is found, it should be corrected and the data re-run for that particular test. If no mistake is found, the test can be run one additional time. If the test limits still are not met, the process step in question must be re-characterized.
The next set of data required is the actual final electrical test data on each lot of parts run. The entire lot should be tested prior to separating parts out for the mechanical test, allowing electrically failed parts to be used for the mechanical test. Mechanical test parts can be taken after electrical test data has been completed and compiled (Table 2). The electrical test data should be as good or better than similar products built on other lines.
A final white paper must be supported by the actual mechanical and electrical test data from each test prior to said data being condensed for the charts. Once white paper data has been assembled and approved, the process is frozen and cannot be changed. Assuming a process, tool, machine or material requires change, a separate mini-characterization will be required.
Summary
The white paper format is a vehicle to provide detailed information on a proposed process or process change. When used in an automatic assembly line, optimum repeatability is assured assuming no changes are implemented. If changes are required, additional experiments, data collection and even an amended white paper may be required. Although the paper is driven by process engineering, anyone affected by the process or change should be involved.
Reference
1. J. Angeloni, "The Missing Reliability Link on Manufacturing Lines," Advanced Packaging, May, 1999.
JIM ANGELONI, vice president of manufacturing services, can be contacted at Natel Engineering Co. Inc., 9340 Owensmouth Ave., Chatsworth, CA 91311; (818) 734-6500; Fax: (818) 734-6530; E-mail: [email protected].
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Table 1. Data for an MCM consisting of chip and wire and epoxy die attach. The substrate material is FR4. The table presents those points in the process that are most vital.
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Table 2. Blank sample table for recording electrical test results.